Plant genomes
encode numerous small molecule glycosyltransferases which modulate the
solubility, activity, immunogenicity and/or reactivity of hormones,
xenobiotics and natural products. The products of these enzymes can
accumulate to very high concentrations, yet somehow avoid inhibiting
their own biosynthesis. Glucosyltransferase UGT74B1
(UDP-glycosyltransferase 74B1) catalyses the penultimate step in the
core biosynthetic pathway of glucosinolates, a group of natural products
with important functions in plant defence against pests and pathogens.
We found that mutation of the highly conserved Ser284 to leucine [wei9-1
(weak ethylene insensitive)] caused only very mild morphological and
metabolic phenotypes, in dramatic contrast with knockout mutants,
indicating that steady state glucosinolate levels are actively regulated
even in unchallenged plants. Analysis of the effects of the mutation
via a structural modelling approach indicated that the affected serine
interacts directly with UDP-glucose, but also predicted alterations in
acceptor substrate affinity and the kcat value, sparking an interest in
the kinetic behaviour of the wild-type enzyme. Initial velocity and
inhibition studies revealed that UGT74B1 is not inhibited by its
glycoside product. Together with the effects of the missense mutation,
these findings are most consistent with a partial rapid equilibrium
ordered mechanism. This model explains the lack of product inhibition
observed both in vitro and in vivo, illustrating a general mechanism
whereby enzymes can continue to function even at very high
product/precursor ratios.

Ophioviridae,The Ophioviridae is a family of filamentous plant viruses, with single-stranded negative, and possibly ambisense, RNA genomes of 11.3–12.5 kb divided into 3–4 segments, each encapsidated separately. Virions are naked filamentous nucleocapsids, forming kinked circles of at least two different contour lengths. The sole genus, Ophiovirus, includes seven species. Four ophioviruses are soil-transmitted and their natural hosts include trees, shrubs, vegetables and bulbous or corm-forming ornamentals, both monocots and dicots. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the which is available at http://www.ictv.global/report/ophioviridae.

We identified and analyzed 33 and 29 IQD1-like genes in Arabidopsis thaliana and Oryza sativa, respectively. The encoded IQD proteins contain a plant-specific domain of 67 conserved amino acid residues, referred to as the IQ67 domain, which is characterized by a unique and repetitive arrangement of three different calmodulin recruitment motifs, known as the IQ, 1-5-10, and 1-8-14 motifs. We demonstrated calmodulin binding for IQD20, the smallest IQD protein in Arabidopsis, which consists of a C-terminal IQ67 domain and a short N-terminal extension. A striking feature of IQD proteins is the high isoelectric point (~10.3) and frequency of serine residues (~11%). We compared the Arabidopsis and rice IQD gene families in terms of gene structure, chromosome location, predicted protein properties and motifs, phylogenetic relationships, and evolutionary history. The existence of an IQD-like gene in bryophytes suggests that IQD proteins are an ancient family of calmodulin-binding proteins and arose during the early evolution of land plants. Comparative phylogenetic analyses indicate that the major IQD gene lineages originated before the monocot-eudicot divergence. The extant IQD loci in Arabidopsis primarily resulted from segmental duplication and reflect preferential retention of paralogous genes, which is characteristic for proteins with regulatory functions. Interaction of IQD1 and IQD20 with calmodulin and the presence of predicted calmodulin binding sites in all IQD family members suggest that IQD proteins are a new class of calmodulin targets. The basic isoelectric point of IQD proteins and their frequently predicted nuclear localization suggest that IQD proteins link calcium signaling pathways to the regulation of gene expression. Our comparative genomics analysis of IQD genes and encoded proteins in two model plant species provides the first step towards the functional dissection of this emerging family of putative calmodulin targets.